Tap-changing system



June lfi, 1931. w. R. FARLEY 1,

TAP QHA'NGING SYSTEM Filed July '31. 1929 INVENTOR William R. Fa rleY 'A'ITORNEY Patented June 16, 1931 UNITED STATES PATENT OFFICE WILLIAM B. IARLEY, F WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC ,& MANUFACTURING COMPANY, A GORPQBATION OF PENNSYL- VANIA.

'rar-cmn'ome SYSTEM Application filed. July 31,

My invention relates to tap-changing systems for transformers and more particularly to the automatic control of the ratio of voltage transformation of a transformer used to connect two power systems.

The practice of interconnecting large power systems necessitates the use of transformers equipped with tap-changing mechanism which functions to vary the ratio of transformation between the interconnected systems as desired. Such points of interconnection are fre uently so located that automatic control 0 the tap-changing system is desirable.

My invention provides for so automatically controlling the operation of the tap-changing mechanism of a transformer for interconnecting two power systems as to maintain the ratio of the number of, effective turns in the primary and secondary windings of the interconnecting transformer substantially equal to the ratio between the voltages of the systems, that is, to'maintain a condition in which there is substantially no interchange of 'wattless or reactive current between twointerconnected systems.

An object of my invention is toprovide for automatically operating a tap-changingmechanism of a transformer used to interconnect two power systems, to'so vary the ratio of voltage transformation as to prevent or limit the flow of wattless or reactive current in the two systems.

In achieving the purpose of myk invention I provide means for varying t e who of transformation in a transformer connected n between two power systems in accordance with the value and character of the wattless or reactive current flowing in one of. the systems.

I pro ose to do this by employing a motoroperate tap-changing mechanism that is I controlled by a regulatingrelay having two opposed windings. One of the windings 1s 5 energized in accordance with the voltage of one system, and the other winding is energized in accordance with the vector sum of a voltage com onent that 1s roportional to the volta e 0 that system an a voltage component t at is proportional to the reuctive 1929. Serial No. 382,460.

current of that system. For the purpose of compensating for ohmic or line drop in voltage, avoltage component may be introduced into the circuit of one relaywinding that depends upon the power component of current and the direction of power flow in the system.

My invention will be better understood by reference to the accompanying drawing in which the single figure is a diagrammatic view of apparatus and circuits employed in one embodiment of my invention.

Referring to the drawing, two ower lines 1 and 2 are connected to the win ings 3 and 4, respectively, of a transformer 5, through which power may be transmitted, in either direction, between the power lines. Since it is desired to maintain the ratio of effective turns in the windings of the transformer 5 substantially equal to the ratio between the voltages of the power lines 1 and 2, a plurality of voltage taps 6 to 10, inclusive, areprovided on one winding 4 of the transformer 5, and tap-changing means, here illustrated as comprising a movable contact arm 11, is provided for varyin the number of effective turns in that win ing by changing the connection of one conductor of the power line2 to the transformer winding, through a selected one of the taps 6 to 10, inclusive. The contact arm 11 is illustrated as being mounted on the pivot 12 and as provided with a gear segment 13 that engages a worm gear 14 driven by a shaft 15. The shaft '15 is driven in the one or in the other direction by a motor 16 through a train of gears 17 and 18, thus operating the contact arm 11 to vary the number of effective turns in the winding 4 of the transformer 5.

When the ratio of transformation of the transformer is the same as the ratio of the voltages'of the two systems, the voltage per turn in each winding of the transformer will be the same, and there will be no interchange of reactive current between the two systems. In the event, however, that the 'voltage per turn of the winding 4 connected appreciably less than the voltage per turn of the winding 3, there will be a leading current in system 2 and a lagging current in system 1.

The motor 16 is lllustrated as energized from three-phase supply conductors 19, 20 and 21 to operate in the one or the other direction, upon the operation of the one or and 23 to a circuit-closing position. The energization of switches 22 and 23 is selectively controlled by a do ble-coil primary, or regulatin relay 24.

The re ay 24 comprises two opposed operating coils 25 and 26 which are so arranged as to actuate a movable contact member 27 into engagement with the one or the other of closing position.

The winding 26 may be energized by a voltage that is proportional to the voltage. of the system 2 and, as illustrated, a compensator 30 may be provided for introducing a voltage component into the circuit of the winding 26 that is proportional to the power component of the load current and is added in a direction dependent upon the direction of the power flow 1n system 2.

The winding 25 is energized by a voltage that is the vector sum of a voltage component that is proportional to the voltage of system 2 and a voltage component that is proportional to the reactive current in system 2. A compensator 31 is provided for introducing a voltage into the circuit of the winding 25 that is proportional to the reactive current.

The compensator 30 ma be of any suitable well known form an is illustrated as comprising a continuous magnetic circuit 32 and two w1ndings 33 and 34 respectively disposed on opposite legs thereof. When the winding 33 is energized, it impresses a voltage upon the winding 34 that is in phase with the current in power circuit 2.

The compensator 31 may also be of any suitable well known form and, for convenience, is illustrated as comprising a magnetic circuit 35 having an air gap 36 therein and two windings 37 and 38 respectively disposed on opposite legs thereof. When the winding 38 is energized, it impresses a voltage upon the winding 37 that is in quadrature with the current in the power circuit 2.

Winding 38 of the compensator 31, and

winding 33 of the compensator 30, are connected in series-circuit relationship with, and are energized from, the secondary windin of acurrent transformer39 that is connecte in system 2. This circuit may be traced from the current transformer 39, through conductor 40, winding 38, conductor 41, windmg 33 and conductor 42, to the current transformer 39.

The windings 25 and 26 are energized from the potential transformer 43 by a voltage that is proportional to the voltage of system 2. The .wlnding 37 of the compensator 31 is connected in series-circuit relationship with the winding 25 of relay 24. This circuit may be traced from one side of the secondary the other of circuit-controlling switches 22- winding of the potential transformer 43, through conductor 44, winding 37, conductor 45, winding 25, conductor 46, an adjustable resistor 47, conductor 48, and conductor 49, to the other side of the secondary winding of the potential transformer 43.

The winding 34 of the compensator 30 is connected in series-circuit relationship with the Winding 26 of the relay 24. This circuit may be traced from one side of the secondary winding of the potential transformer 43, through conductor 44, conductor 50, an adjustable resistor 51, winding 26, conductor 52, winding 34 and conductor 49, to the other side of the secondary winding of the potential transformer 43.

The resistors 47 and 51 are so adjusted that the force exerted on each of the windings 25 and 26 will be balanced when the desired voltage ratio of transformation, corresponding to a desired power factor, exists. If we neglect the compensation for ohmic drop in voltage on the line and assume that the resistors 47 and 51 are adjusted to maintain unity power factor, then, for any voltage ratio between the power systems 1 and 2, the forces exerted by the windings 25 and 26 will be balanced when the contact arm 11 is on such tap connection that the voltages per turn of the respective transformer windings are substantially equal.

The operation of my system is as follows:

The voltage impressed upon the winding 25 of relay 24 is the vector sum of a voltage that is proportional to the voltage of system 2 and a voltage that is proportional to the reactive component of the current in system 2. The voltage impressed upon the winding 26 will be a voltage that is proportional to the voltage of system 2, compensated by the voltage impressed on winding 34 of the compensator 30, which is proportional to the ohmic component of the current in system 2.

Let us assume that the resistors 47 and 51 haie been so adjusted that the relay 24 is in a neutral or balanced position when the power factor of the system 2 is substantially unity, and the voltage ratio of the power ging with respect to voltage, and the reactive component of the load current will increase. The winding 37 is so connected in the circuit of the winding that, under this condition, the vector sumof the voltages that are impressed upon the winding 25 decreases. The pull exerted by the winding 26 is then greater than the pull exerted by the winding 25, and the movable cont-act member 27 engages the stationary contact members 29, thereby completing a circuit to actuate switch 23 to a circuit-closing position to operate the motor 16 and so actuate the tapchanging mechanism as to move-the contact arm 11 toward the tap 6. The switch-controlling circuit may be traced from the supply conductor 19, through conductor 53, conductor 54, the operating coil of switch 23,

conductor 55, the engaged contact members 27 and 29 and conductor 56, to the supply conductor 20.

than the voltage per turn of winding 3, andthe current will be leading with respect to the voltage. The vector sum of the voltages that are impressed upon the winding 25 will increase, and the pull exerted by the.

winding 25 will be greater than the pull exerted by the winding 26. This will cause the movable contact member 27 to engage the stationary contact members 28 and complete a circuit to actuate the switch 22 to a circuit-closing position, This circuit may be traced from the supply conductor 19, through conductor 53, conductor 63, the operating coil of the switch 22, conductor 64, the engaged contact members 27 and 28 and conductor 56, to the supply conductor 20.

The actuation of the switch 22 to a circuitclosing position will complete a circuit for operating the motor 16 in a direction to cause the contact arm 11 to move toward the tap 10. This circuit may be traced from supply conductors 19, 20 and 21, through conductors 57, 58 and 59, the contact members of switch 22 and conductors 60, 61 and 62, to the motor 16. This movement of the tap changer toward the tap 10 will decrease the number of turns in-winding 4 until the voltage per turn becomes substantially the same in both windings.

It will be evident from the foregoing disclosure anddescription that I have provideda tap-changing system for automatically maintaining the ratio of transformation of bodiment of my invention only. Since, however, many modifications within the s irit and scope of my invention may occur to t ose skilled in the art, I do not wish to be limited otherwise than by the scope of the appended claims.

I claim as my invention 1. An automatic tap-changing system for transformers comprising, in combination, a plurality of power lines, a transformer connecting said power lines, said transformer being provided with motor-operated tapchanging equipment, and means associated with one of said power lines and responsive to the reactive component of current in said power line for so controlling the operation of said equipment as to maintain the ratio of transformation substantially equal to the ratio of the voltages of the respective power lines.

2. In combination, a plurality of power lines, a transformer connecting said power lines, motor-operated tap-changing means associated with said transformer, and means responsive to the reactive component of current in one of said power lines for actuating as I said tap-changing means for maintaining the ratio of transformation of the transformer substantially the same as the ratio of the voltages of the power lines.

3. In an automatic control system, a trans former, tap-changing equipment therefor, a

plurality of power lines connected to, said I transformer, and means for operating the tap changer for maintaining the ratio of transformation of said transformer equal to the ratio of the voltages of the said connected power lines, said means being responsive to the reactive component of current in one of a motor-operated tap changer for maintaining a constant ratio between the effective turns of the two windings, a relay for controlling the operation of-said motor, said relay having a plurality of windings, and means for ener izing one of said windings by a voltage t at is the vector sum. of a volta e proportional to the voltage of. one of sa1d power lines and a voltage that is proportional to the reactive component of current of said power line.

6. In combination, a transformer havin Q primary and. secondary windings, said win ings being connected to two different power lines, a motor-operated tap changer for maintaining the ratio of transformation equal to the voltages of the respective power lines, a m relay for automatically controlling the operation of said motor, said relay having a plurality of windings, and means for energizing the relay windings in accordance with the voltage of, and the amount of reactive ourrent in, one of said lines.

7. In combination, a plurality of power lines, a transformer interconnecting said power lines and having primary and secondary windings, a motor-operated tap changer for varying the ratio of voltage transformation of said transformer, an automatic control system for said motor including a relay having two opposed windings, means for energizing said relay windings in accordance with the voltage of one of said power lines and means for compensating the energization of said relay windings, respectively, in accordance with the reactive component of current in said line and in accordance with the ohmic component of current in said line.

8. In combination, a plurality of ower lines, a transformerinterconnecting sai power lines and having primary and secondary windings, a motor-operated tap changer for varying the ratio of voltage transformation of said transformer,-an automatic control system for said motor including a relay having two opposed windings, means for energizing said relay windings in accordance with the voltage of one of said power lines, and means for compensating the energization of one of said windings in accordance with thr reactive component of current in said line.

9. In combination, a plurality of power lines, a transformer interconnecting said power lines and having primary and secondary windings a motor-operated tap changer for varying the ratio of voltage transformation of said transformer, an automatic control'system for said motor comprising a contact-making relay, and means for actuating said relay to operate said tap changer in the one, orin the other, direction in accordance with the flow of wattless current in one of said .power lines. 9

In testimony whereof, I have hereunto subscribed my name this eleventh day of July,

WILLIAM R. FARLEY. 

